Method and device for signal protection

ABSTRACT

Method for decreasing the existence of externally detectable revealing signals, so-called {umlaut over (ROS)}, from keyboards ( 1 ), e.g. for computers, where the keyboard is fed with signals, so-called matrix signals, which are detected for detection of activity regarding the keys ( 2 ) of the keyboard, whereby said matrix signals are generated by means of signal devices. The method is especially characterized in that the matrix signals are high-frequency filtered before they are fed to the keyboard.

[0001] The present invention relates to a method for decreasing thepresence of externally detectable revealing signals, so-called {umlautover (ROS)}, from keyboards, e.g. for computers, where the keyboard isfed with signals, so-called matrix signals, which are detected fordetecting activity regarding the keys of the keyboard, whereby saidmatrix signals are generated by means of a signal device/signal devices.

[0002] The invention also regards a device for carrying out the method.

[0003] Earlier, attempts have been made to decrease {umlaut over (ROS)}from keyboards by a certain encapsulation of the signal devices by meansof the keyboard's own encapsulation and by screening of cable devicesfor the transfer of signals to devices for detection, such as a computerfor transformation in a way known per se, to signs, commands or thelike, generated by means of the keyboard.

[0004] Normally, {umlaut over (ROS)} do not originate from said matrixsignals, which are usually made of signals of certain, comparatively lowbasic frequencies, basic tones, but from over-frequencies, harmonics,which are generated at the same time as the basic frequencies and whichare externally detectable to a considerably greater extent than thebasic frequencies. {umlaut over (ROS)} can also come from digitalasynchronous serial signals, which comprise information about activityregarding the keys of the keyboard and are the result of atransformation by means of the signal devices for further transfer todevices for detection, such as a computer. Thus, by means of techniqueused up to now, one has not been able to decrease the externallydetectable signals to an acceptable extent.

[0005] However, according to the present invention, the presence ofexternally detectable signals can be decreased to an extraordinary lowlevel or practically be eliminated.

[0006] Thus, the present invention relates to a method according to theintroductory part of the attached patent claim 1. The method isespecially characterized by what is specified in the characterizing partof said patent claim.

[0007] The invention further relates to a device according to theintroductory part of the attached patent claim 11. The device isespecially characterized by what is specified in the characterizing partof the last mentioned patent claim,

[0008] In the following, the invention will be described in more detailin connection with exemplifying embodiments and the attached drawings,where

[0009]FIG. 1 schematically shows a first embodiment of a deviceaccording to the invention, where the keyboard is shown towards theupper side of its main extension plane, and

[0010]FIG. 2 schematically shows a section A-A according to FIG. 1.

[0011]1 in FIG. 1 designates a keyboard with keys 2, shown towards itsupper side. Activities regarding the keys of the keyboard are intendedto be detected in the usual way by means of, preferably continuous,feeding of the key arrangement with matrix signals via matrix wires 3and preferably continuous detection of said matrix signals. Here, thematrix wires as well as the key arrangement are shown schematically.

[0012]4 designates signal devices arranged for the generation of saidmatrix signals, where the signal devices preferably are included in anelectronics card. The signal devices 4 are arranged in a high-frequencytight container 5, which in the design shown is an external separateunit 5, arranged to be connected to the keyboard via an interface 6comprising a connector 7 for outgoing matrix signals, to which matrixwires are connected. The connector 7 comprises filter devices 7′,arranged to high-frequency filter generated matrix signals as well asdigital serial signals so that the harmonics of the signals are stronglyattenuated or completely removed. Said digital serial signals are, asmentioned, the result of a transformation of the “response” of thekeyboard to matrix signals, where the transformation is intended to bedone by means of the signal devices.

[0013] According to the embodiment shown, the matrix wires 3 run fromthe interface to a connection means 8, from which matrix wires run outinto the key arrangement, which hereby is arranged to be fed withhigh-frequency filtered matrix signals. The connection means is intendedto replace the connection function of the signal devices, which functioncannot be used for the matrix wires when the signal devices are placedin the container 5.

[0014]9 designates a metallic earth plane, upon which the keyarrangement with matrix wires etc. is placed and which is connected toearth by a good, powerful earth connection 10. According to the designshown, the earth plane is connected to an earth plane 11 of theconnection means, which earth plane in its turn is connected to theHF-tight container, by a powerful earth connection 12. According topreferred embodiments, the wires 3 for the matrix signals are preferablycarried by means of a plastic foil 3′ and arranged close to the earthplane/planes 9, 11, in order to obtain the best earthing effectpossible.

[0015] For transfer of signals from the keyboard to e.g. a computer, adouble-screened cable 13 is provided, which is connected by a connectionbushing 14 with a 360° screen connection to the container 5 and arrangedto be connected to e.g. the HF-tight chassis of a computer by means of ascreened contact means 15 with a 360° screen connection (not shown).

[0016] The method according to the invention as well as the function ofthe device according to the invention should to a considerable extent beobvious from the above.

[0017] Externally detectable signals in the form of, primarily,harmonics generated by means of the matrix signals and the serialdigital signals of the signal devices are thus screened by means of theHF-tight container 5 and filtered in the interface 6 in order not to befed into the matrix wires. Remaining harmonics of the signal, whichsignal is fed to the matrix of the keyboard and which must be digital inorder to be interpretable, are screened by means of the earth plane 9 ofthe keyboard, which earth plane acts as an open screen container. Bymeans of the powerful earth cables 10, 12, screening of such remainingharmonics is done which otherwise could be detected externally. TheHF-tight cables 13 and connection means 14, 15 function as an HF-tightextension of the HF-tight chassis of the computer or the corresponding.

[0018] Thus, by the arrangement described, a keyboard includingconnection has been achieved, which substantially does not emit {umlautover (ROS)} to a detectable extent

[0019] Above, the invention has been described in connection with mainlyone example of embodiment, Of course, further embodiments as well asminor changes and additions may be contemplated without deviating fromthe general inventive idea.

[0020] Thus, per se, it is conceivable to arrange the screening of thesignal devices in the keyboard, i.e. by at least one HF-tight containerarranged in the keyboard.

[0021] Thus, the invention should not be considered to be limited to theabove described embodiments but may be varied within the frame specifiedby the attached patent claims.

1. Method for decreasing the presence of externally detectable revealingsignals, so-called ROS, from keyboards (1), e. g. for computers, wherethe keyboard is fed with signals, so-called matrix signals, which aredetected for detection of activity as regards the keys (2) of thekeyboard, whereby said matrix signals are generated by means of signaldevices, characterized in that the matrix signals are high-frequencyfiltered before being fed to the keyboard.
 2. Method according to claim1, characterized in that the matrix signals i.a. are generated by meansof the signal devices (4) in a screening encapsulation (5) andhigh-frequency filtered in an interface (6) between said encapsulationand the keyboard.
 3. Method according to claim 2, characterized in thatfiltering takes place in a contact means (7) between the keyboard andthe screening encapsulation.
 4. Method according to claim 2,characterized in that the screening encapsulation is arranged as aseparate unit (15), which is connected to the keyboard.
 5. Methodaccording to claim 2 characterized in that a metallic earth plane (9) isarranged in the keyboard and connected to the screening encapsulationand preferably to the earth of a computer provided.
 6. Method accordingto claim 1, characterized in that filtering is done to a suitable extentof over-frequencies of i.a. the basic frequencies of the matrix signals.7. Method according to claim 1, characterized in that the filteredmatrix signals are fed to the keyboard via a connection means (8). 8.Method according to claim 7, characterized in that the earth plane ofthe key board is connected to the screening encapsulation via an earthplane (11) of the connection means.
 9. Method according to claim 5,characterized in that wires (3) for the matrix signals are preferablycarried by means of a foil (3′), preferably of plastic, and arrangedclose to the earth plane provided.
 10. Method according to claim 1,characterized in that digital serial signals, comprising informationabout activity regarding the keys of the key board, are generated bymeans of the signal devices for further transfer to de vices fordetection, e. g. a computer, whereby also said digital signals are highfrequency filtered as far as i.a. leakage to the keyboard is concerned.11. Device for decreasing the presence of externally detectablerevealing signals, so called ROS, from keyboards, e.g. for computers,where the keyboard is arranged to be fed with signals, so-called matrixsignals, intended to be detected for detection of activity as regardsthe keys of the keyboard and where signal devices are arranged togenerate said matrix signals, characterized by filtering devices (7′)for high-frequency filtering of matrix signals before these signals arefed to the keyboard (1).
 12. Device according to claim 11, characterizedby a screening encapsulation (15) for said signal devices (4), in whichi.a. the matrix signals are intended to be generated, and by aninterface (6) between the encapsulation and the keyboard, in whichinterface filtering devices for high-frequency filtering of i.a. matrixsignals are provided.
 13. Device according to claim 12, characterized bya contact means (7) between the keyboard and the screening encapsulationcomprising said filtering devices.
 14. Device according to claim 12,characterized in that the screening encapsulation is a separate unit (5)arranged for connection to the keyboard.
 15. Device according to claim12, characterized by a metallic earth plane (9) of the keyboard, whichearth plane is connected to the screening encapsulation and, whenapplicable, to the earth of detection devices, e. g. a computer. 16.Device according to claim 11, characterized in that the filteringdevices are arranged, to a suitable extent, to filter awayover-frequencies of i.a. the basic frequencies of the matrix signals.17. Device according to claim 11, characterized by a connection means(8), via which filtered matrix signals are intended to be fed to thekeyboard.
 18. Device according to claim 17, characterized by an earthplane (11) of said connection means, via which the earth plane of thekeyboard is preferably intended to be connected to the screeningencapsulation.
 19. Device according to claim 11, characterized by aconnection bushing (14) with a360 screen connection to the screeningcontainer for a, preferably double-screened, cable (13) arranged to beconnected to the high-frequency tight chassis of a computer by means ofa screened contact means (15) with a360 screen connection.
 20. Deviceaccording to claim 15, characterized in that wires (3) for the matrixsignals are preferably intended to preferably be carried by means of afoil (3), and are arranged close to an earth plane provided.
 21. Deviceaccording to claim 11, characterized in that digital serial signals,comprising information about activity regarding the keys of thekeyboard, are intended to be generated by means of the signal devicesfor further transfer to devices for detection, e. g. a computer, wherebyalso said digital signals are intended to be high-frequency filtered asfar as i.a. leakage to the key board is concerned.